Improvement of water nozzle shape for fire protection based on optimum design

This study is concerning the optimum design of a water nozzle for firefighting equipment used to protect large indoor spaces and high-rise buildings. Water nozzles for such use are required to have a long range of reach and/or a wide coverage. Such performance can be obtained by simply increasing the flow rate, but that is caused substantial pressure loss by the fluid friction within the nozzle and the pipe. The objective of this study is to obtain a water nozzle with minimum fluid friction by optimum design, as a result the size of piping, pump and water reservoir for firefighting equipment can be minimized. The conventional water nozzle used in firefighting is called the smooth bore nozzle, which have a wedge-shape profile whose diameter decreasing toward the exit. However, whether or not this shape is optimum have not been known. In this study, a method is presented to obtain a friction-minimum nozzle profile, while setting the inlet-and outlet-diameters and the length of the nozzle as fixed parameters. It was found that the half-spindle-type nozzle, whose diameter is almost constant along the length but quickly decreases at the exit, shows the smallest friction than the other profiles (i.e. smooth-bore, straight and concaved), therefore showing maximum arrival distance.